US2010/0216773 A1 discloses a method for preparing a phenanthroindolizidine and phenanthroquinolizidine alkaloid, and in Example 1 thereof a mixture of compounds of 13-16 are allegedly synthesized by partial hydrolysis of compound 28, where the structures of the compounds 13-16 and 28 are shown as follows:
These four compounds 13-16 disclosed in US2010/0216773 A1 cannot be obtained by the treatment of compound 28 with sodium bis(2-methoxyethoxy)aluminium hydride, a reducing agent, according to our previous method. [T. H. Chuang, S. J. Lee, C. W. Yang, P. L Wu Org. Biomol. Chem. 2006, 4, 860-867.].